Organic conjugated oligomers and polymers are materials that possess a delocalized pi-electron system along their backbone. These organic materials are subject to important investigations from both academic and industrial laboratories due to their great potential for applications in electronic and opto-electronic devices, such as field effect transistors (OFETs), light emitting diodes (OLEDs) and photovoltaic cells (OPCs). The economical advantages of using organic over inorganic semi-conducting materials in devices include, low cost of synthesis, ease of processing and the extensive tunability range of their optical and electrical properties through chemical modifications.
The vast majority of microelectronic devices are currently based on inorganic semi-conductor materials such as crystalline silicon. For large area devices including flat-panel displays and smart cards, where the use of crystalline silicon is limited by the size of the single crystals, amorphous and polycrystalline silicon are currently used. However, the relatively high temperatures needed, in their fabrication process prevent their utilization with plastic substrates. On the other hand organic materials can be processed at or near room temperature by solution-processing or thermal evaporation on polymeric substrates. Organic-based devices such as OFETs are gaining interest as their performance has increased up to a point that they now compete with their inorganic counterparts. In the short term, it is recognized that organic semi-conductor materials could be used in the production of low-resolution components, such as identification tags, smart cards and pixel drivers for displays. Up to now, only pentacene and regioregular polythiophenes have demonstrated the required performances, but the former is difficult to process and the later is easily oxidized in air.
Additionally, it has long been felt that a technically viable emissive display technology could compete with-the currently dominating technology of liquid crystal displays (LCDs) and OLEDs are today considered to be in the best position to do just that. Current LCDs present limitations such as low efficiency, poor vision angle, and speed and temperature range limitations. OLEDs, however, demonstrate particular promise for displays as they can be tuned to any colour, operate at relatively low voltages with high efficiency and have excellent visual properties. A lot of work is going on in chemistry laboratories to find materials with high luminous quantum efficiency, good colour purity and great stability for the application to OLED displays. While some materials meet or exceed some of the requirements for commercial displays, to date none meets them all.
Furthermore, the need to develop renewable energy sources continues to stimulate new approaches to the conversion of solar energy into electrical energy through the production of photovoltaic devices. Although inorganic semi-conductors such as silicon, amorphous silicon, gallium arsenide and sulfide salts, have been the primary focus of commercial applications, the photosensitivity and the photovoltaic effects in devices made with conjugated oligomeric or polymeric organic materials have also been explored and have shown excellent results. The main advantage of using organic materials in photovoltaic devices is the low-cost of fabrication in large sizes and in desired configurations. As an example, the use of semi-transparent organic thin film on the roof area or between insulating windows could be employed as power generation in new and existing buildings.
Intense research is going on at the chemistry level to find a class of organic materials that could be used in OFETs as well as in OLEDs and OPCs. This new class of organic materials should be easy to synthesis at a low cost and should be easy to tune over a wide range of electrical and optical properties through chemical modifications to meet the entire required criteria for commercialization of OFETs, OLEDs and OPCs.